This application is based on Japanese patent application No. 2001-93907 filed in Japan on Mar. 28, 2001, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and particularly to a liquid crystal display apparatus of a reflection type including liquid crystals, which can selectively reflect light of specific wavelengths in visible light at a room temperature.
2. Description of Related Art
A liquid crystal display apparatus basically has a pair of substrates and a liquid crystal layer held between the substrates. By applying a drive voltage to the liquid crystal layer, orientation of liquid crystal molecules is controlled to modulate external light incident to the liquid crystal layer so that images or the like can be displayed in an intended manner.
Various manners have been proposed for display by the liquid crystal.
In recent years, research has been conducted on a liquid crystal display apparatus using chiral nematic liquid crystal, which is prepared by adding a chiral material to a nematic liquid crystal, and exhibits a cholesteric liquid crystal phase at a room temperature.
It is already known that the liquid crystal display apparatus of the above type can be used as a liquid crystal display apparatus of a reflection type, which utilizes a selective reflectivity of the chiral nematic liquid crystal, and can be driven with a low power consumption.
In this liquid crystal display apparatus of the reflection type, high and low pulse voltages can be selectively applied to switch the liquid crystal between a planar state (colored state) and a focal conic state (transparent state).
Even after the application of such pulse voltages is stopped, the region, which was switched to the planar state, keeps the planar state, and the region, which was switched to the focal conic state, keeps the focal conic state. Thus, a bistability or memory property is exhibited, and thereby the display is maintained even after the stop of application of the voltages.
However, the conventional liquid crystal display apparatus of the reflection type using the chiral nematic liquid crystal cannot yet perform the image display with a sufficiently high reflectance, and therefore cannot achieve sufficiently high contrast between the planar state and the focal conic state.
Further, the conventional liquid crystal display apparatus of the reflection type using the chiral nematic liquid crystal cannot sufficiently perform the display in white because the apparatus basically utilizes the selective reflection characteristics of the visible light.
An object of the invention is to provide a liquid crystal display apparatus of a reflection type, which can display images with high contrast while achieving a good light reflectance in a monochrome display operation.
Another object of the invention is to provide a liquid crystal display apparatus of a reflection type, which can be driven with a low voltage.
Still another object of the invention is to provide a liquid crystal display apparatus of a reflection type, in which a dependence on a viewing angle can be small.
The invention provides a liquid crystal display apparatus including:
a first liquid crystal layer including first liquid crystal exhibiting a cholesteric phase at a room temperature, and being tuned to selectively reflect light of a wavelength xcex1 within a visible wavelength range; and
a second liquid crystal layer disposed on the first liquid crystal layer, including second liquid crystal exhibiting a cholesteric phase at the room temperature, and being tuned to selectively reflect light of a wavelength xcex2 within the visible wavelength range, wherein
a difference between the selective reflection wavelengths xcex1 and xcex2 is in a range from 100 nm to 150 nm.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.